This invention relates to the field of separation in which different fluids are separated by a permeable membrane so that one or more components of one fluid will pass through the membrane to the other fluid, such as in dialysis and desalination. For purposes of illustration the disclosed and claimed invention relates particularly to an artificial kidney system for treating human blood and more specifically to improvements in coil type dialyzers.
Numerous coil dialyzers are presently on the market and generally comprise a central relatively rigid core on which is wound open mesh support material and flattened tubular permeable membrane material. This type of device, however, has a basic problem in that a physical transition must be made in the shape of the membrane material from its rather wide flattened state inside the coil to a gathered, round shape at each end where it is mated with the external tubing connectors. In this transition zone numerous overlapping folds of the permeable membrane material create stagnant areas where dangerous blood clots can form and in some instances actually stop flow of blood. The gathering of the permeable membrane around the tubing connectors during manufacture also substantially increases the chance of puncturing or tearing the membrane creating dangerous leakage paths between dialysate and blood. The gathering also can create excess thicknesses which prevent a proper seal with the tubing connector introducing yet another leakage path.
One approach taken by the prior art to minimize the effects of gathering membrane tubing around tubing connectors is illustrated in Miller U.S. Pat. No. 3,508,662 issued Apr. 28, 1970. The Miller patent discloses an enlarged tubing connector to minimize the number of folds in the permeable membrane as it is gathered around the tubing connector, but even this commercially successful approach does not completely obviate the aforementioned problems.
Another disadvantage of gathering the permeable membrane material around the tubing connectors is that of the excess fluid weight in the permeable membrane tubing pulling on the connector which opens up leakage paths and accelerates tearing of the membrane. This problem is illustrated in FIG. 5 of the Miller '662 patent which shows a large area of tubing full of blood hanging from the tubing connector. This weight coupled with pulsations from the blood pump creates a dangerous propensity for leakage.
Another prior art device which has addressed itself to some of these problems is a dialyzer made by AMCO, Model DC-7. This device contains a flattened channel with preformed tubing connectors therein which is heat molded onto the ends of the flattened permeable tubing. While this avoids the problem associated with gathering the permeable tubing around a connector the channel is quite bulky and the need for heat to mold the channel around the permeable membrane tubing substantially increases the likelihood of leakage in the tubing. Also this device does not solve the problem of the weight of blood pulling on the tubing connector.